I’d like to address this in two parts: Potential harm that is (1) major versus (2) subtle of various PEMF Products:
By Potential “Major Harm”, I mean the potential of causing injury or death that anyone would immediately appreciate: heart attacks, electrical burns, severe nerve damage, major tissue lesions or tumors or the promotion of sepsis, etc.
Potential Major Harm: As far as I know, PEMF products are not generally causing major harm to people. Even the ultra-powerful ones tend to be pretty harmless (when used correctly). Otherwise, there would be major product recalls and many scientific and clinical reports on this topic, but there are not. I have read every scientific paper in every language on the topic of PEMF, including clinical case studies, and I have never heard of a case of PEMF used correctly causing this type of harm.
By Potential “Subtle Harm”, I mean those injuries not yet generally appreciated by mainstream medicine, such as the type of harm reported by people with EMI sensitivity, and things of a similar nature.
Subtle Harm is, by its nature, very difficult to detect and to prove. Just as a matter of common sense, the approach should be to remove all known types of electromagnetism from the PEMF signal that are not biologically beneficial. I have been able to show, and have written extensively about, the fact that it is possible to remove at least 99% of the power from typical PEMF pulses and still retain full biological benefit. So, what, exactly, was the remaining 99% of the power doing? Nothing beneficial, maybe something harmful. Its hard to say for sure, but that energy is definitely not needed, and confers no benefit, so it should be removed from all PEMF waveforms.
This is precisely what I have done over the past 25 years, and it is why I trademarked ICES-PEMF, so that I could have technical control over the use of a specific term (ICES) that identifies that product that uses a biophysically efficient and effective waveform.
Unfortunately, that means that the advertised “power” of a PEMF product is not a very good guide to whether it is safe or not from the standpoint of “subtle harm”.
SUMMARY:
When looking to avoid potentially harmful PEMF products, generally you do not need to worry to much about obvious, major harm, since there seems to be very little evidence of this type of danger. If your concern is subtle harm, for example if you are EMI sensitive, then you need to be much more concerned with waveform rather than power (Gauss level). So, if this is your primary concern, I would steer away from any of the high-power systems they call “ringers”, which are often advertised as using “Spark Gap Technology!!”, because spark gap technology is very very old, cheap and crude. It predates even vacuum tubes, and generates very powerful, but very inefficient and “dirty”, electro-magnetic pulses.